Frequency diversity is employed to counter selective fadings as a result of multi-path propagation for troposcatter and short-wave connections for digital useful signals employing frequency modulation. For this purpose, the digital useful signal is supported on a frequency arrangement comprising at least three radio frequencies in that the digital useful signal, together with at least one additional oscillation, and, in fact, an additional fundamental oscillation which determines the frequency of the spacing in radio-frequency frequency arrangement, is fed to the input of a frequency modulator. At the input end, the radio-frequency carriers of the frequency arrangement, which are each modulated with the useful signal, are all converted by coherent mixing into the same frequency level, from which, by way of a combiner, a sum signal is obtained which is the optimum in respect of signal-to-noise ratio.

Digital radio system

The present invention provides a method and apparatus for detecting and compensating for transmitter phase shift in a radio transmitter. A local oscillator generates a local oscillator signal. A modulator such as an I/Q modulator modulates input signals onto the local oscillator signal to generate a forward signal. That forward signal is amplified and otherwise prepared for transmission via an antenna. The transmitted signal is detected, and a phase adjuster substantially continuously detects and cancels undesired phase shifts in the detected signal caused by elements in the radio chain. A specific, example embodiment of the present invention is provided in a Cartesian feedback system wherein the phase of the feedback signal is detected and aligned with the phase of the original modulated signal, providing uncorrupted I and Q baseband feedback signals. Another specific example embodiment of the present invention is to a diversity radio receiver. Received signals from the diversity antennas are processed to determine the phase difference between the two signals. The phase of one of the received signals is rotated to match the phase of the other, and thereafter, the diversity received signals are added together before demodulating the originally transmitted signal. Such additive combination of diversity received signals under same or similar received signal level conditions when two signals are aligned in phase considerably improves the signal to noise ratio of the received signal.

Method and apparatus for detecting and compensating for undesired phase shift in a radio transceiver

A dual mode cellular radiotelephone subscriber unit (802) comprises a diversity receiver (812) and a controller (814). The diversity receiver (812) receives either a first radio frequency (RF) signal (808) modulated by a digital modulation method (805) or a second RF signal (810) modulated by an analog modulation method (807). In one embodiment, the controller (814) controls the diversity receiver (812) responsive to a first diversity algorithm (834) when the diversity receiver (812) receives the first RF signal (808) modulated by the digital modulation method (805), and responsive to a second diversity algorithm (836) when the diversity receiver (812) receives the second RF signal (810) modulated by the analog modulation method (836). In another embodiment, the controller (814) controls the diversity receiver (812) responsive to a first received information set (835) when the diversity receiver (812) receives the first RF signal (808) modulated by the digital modulation method (805), and responsive to a second received information set (837) when the diversity receiver (812) receives the second RF signal (810) modulated by the analog modulation method (807).

Dual mode radio subscriber unit having a diversity receiver apparatus and method therefor

A spatial diversity system for digital mobile telephone networks which comprises at least two antennas, one antenna being part of a primary (or master) unit and the other being part of a diversity (or slave) unit, each unit having processing means to detect the "quality" of digital audio signals received by their respective antennas, the "quality" comprising link quality, AGC level and parity errors; the primary unit being capable of comparing the "quality" of the audio signals received by each antenna, selecting the higher "quality" signal and transmitting the higher "quality" signal to the telephone network.

Combination spatial diversity system

An antenna diversity system comprises at least two antennas (202, 212). In a first embodiment each antenna is connected via a common connection point (222) to a receiver (224), by means of a respective switch (204, 214) which presents a low impedance connection between the antenna and receiver in the on state and a substantially reactive load (210, 220) to the antenna (202, 212) in the off state. Selection of appropriate impedances for the off state load enables the antennas (202, 212) to function as an array with a variety of beam patterns depending on the state of the switches (204, 214). Cycling through a sequence of switch states steers the antenna beam providing improved resistance to fading and multipath effects. In a second embodiment the antennas are connected to a hybrid coupler, which enables two beam patterns to be available simulaneously for signal quality measurement and comparison.

Antenna diversity system

A space diversity receiving system is described which eliminates the low frequency phase modulation component at the intermediate frequency stage output. Received signals from two antennae are converted to intermediate frequency signals and then combined after one signal has been passed through a variable phase shifter. Branching amplifiers are provided in each intermediate frequency channel so that all phase modulation, phase detection and production of the control signal necessary for controlling the variable phase shifter are achieved outside of all main intermediate frequency channels that are to be combined to obtain an intermediate frequency output.

Space diversity receiving system with phase-controlled signal combining at intermediate frequency stage

A diversity receiving system having a hysteresis switching characteristic has first and second signal receiver portions supplied with at least one radio frequency signal for producing a pair of received signals, a level detection circuit provides a pair of voltages representative of the levels of the received signals, the outputs of the level detection circuit are compared to determine which one is at a higher level, a switching circuit selectively leads the higher level one of the received signals to an output terminal of the receiving system, and the level of the higher level one of the received signals is raised with respect to the lower level one which has not been led to said output terminal. In the present system, the higher level signal is selected while the reference level for detection with respect to the higher level signal is relatively lowered so that the higher level signal is more stably selected. Then, if the input signal of the unselected receiver is later selected, the reference level for detection thereof is relatively lowered. This results in alternate lowering of the reference level for detection at the detection circuit. As a result, the frequency of the switch-over is reduced while the reception is equally shared by the two receivers, maintaining the high quality of reception.

Kyo Kinoshita

Papers

Space diversity receiving system with phase-controlled signal combining at intermediate frequency stage

Diversity receiving system